Vinayak Bhanu - Academia.edu (original) (raw)

Papers by Vinayak Bhanu

Polymer, 2003

The effects of methyl acrylate (MA) incorporation (0-15 mol%) on the glass transition, melting be... more The effects of methyl acrylate (MA) incorporation (0-15 mol%) on the glass transition, melting behavior, and the peak temperature of the stabilization exotherm in acrylonitrile (AN) based copolymers were studied. A qualitative decrease in crystalline content with increasing MA content was observed using wide angle X-ray scattering (WAXS). The lower crystallinity of the high MA content copolymers could also be noted by the magnitudes of the modulus drop at T g using dynamic mechanical analysis (DMA) and the step change in heat capacity at T g using differential scanning calorimetry (DSC). The DSC and differential thermal analysis (DTA) results indicated that the melting temperature of the copolymers decreased with increasing MA content. The magnitude of the crystallization exotherms decreased with successive melting/crystallization cycles. DTA experiments demonstrated that the stabilization reaction, which transforms polyacyrlonitrile into an insoluble, rigid structure, is delayed by the presence of the comonomer.

Journal of Applied Polymer Science, 2006

ABSTRACT A systematic study of the synthesis and characterization of 3,3′-disulfonated-4,4′-dichl... more ABSTRACT A systematic study of the synthesis and characterization of 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone (SDCDPS) monomer was conducted by varying reactant stoichiometries (molar ratios of 4,4′-dichlorodiphenyl sulfone (DCDPS) to SO3 1 : 2.2, 1 : 2.9, and 1 : 3.3), reaction temperature (90–120°C), and reaction time (4–6 h). The optimum synthesis batch process variables were 1 : 3.3 reactant molar ratio (DCDPS : SO3) at 110°C for 6 h. In earlier studies, recrystallization of the “crude” disulfonated monomer from alcohol–water mixture was necessary to remove the monosulfonated and DCDPS impurities that lowered yield. However, in the current research, SDCDPS was successfully synthesized at nearly 100% conversion, which effectively eliminated the need for recrystallization. Recrystallization of SDCDPS from several alcohol–water mixtures (methanol–, ethanol–, and isoproponal–water mixtures) was investigated to compare product purities. Several characterization methods including proton NMR, HPLC, UV–visible, and fast atom bombardment mass spectroscopy confirmed that the crude SDCDPS was completely disulfonated and identical to recrystallized SDCDPS, without having any monosulfonated or starting material DCDPS impurities. Hence, it was demonstrated that the crude SDCDPS monomer by the current one-step process and the recrystallized SDCDPS monomer were identical. This optimized monomer synthesis has been used to scale up the SDCDPS and poly(arylene ether sulfone) random and statistical copolymers at controlled disulfonation (35 and 45 mol %) levels, which were then used to fabricate proton exchange membranes for fuel cell applications. The intrinsic viscosity data confirmed that high molecular weight film forming copolymers were synthesized. The calculated degree of disulfonations by proton NMR was in close agreement with target disulfonations. It may be concluded that this optimized SDCDPS synthesis eliminates the need for recrystallization, which would be expected to improve process economics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4595–4602, 2006

Journal of Applied Polymer Science, 2002

This work is concerned with the feasibility of achieving melt-processable polyacrylonitrile copol... more This work is concerned with the feasibility of achieving melt-processable polyacrylonitrile copolymer systems as precursors for the manufacture of carbon fibers. Identification of suitable comonomers and achieving the optimum content of the comonomer were some of the main objectives of this investigation. It was seen that methyl acrylate (MA) was found to be suitable for enabling the melt processing of polyacrylonitrile (PAN), in terms of melt viscosity, time stability, and char yield. Below 10 mol % of MA, the PAN copolymer exhibited no flowability, even at very low molecular weights (ϳ 20,000). The long-range order inherently present in PAN is speculated to be broken down at a critical value of about 10% MA at 220°C in the PAN-based system, enabling its melt flowability. It was also seen that the incorporation of MA was seen to improve the temperature and molecular weight window of processability of the PAN system. The molecular weight cutoff for the 90/10 mol % acrylonitrile/methyl acrylate (AN/MA) system was about 50,000 at 220°C, whereas it was increased to about 100,000 in the presence of 15 mol % MA comonomer. Feasibility studies on the use of other comonomers such as higher acrylates and acrylamides were also conducted.

Journal of Polymer Science Part A: Polymer Chemistry, 2003

Poly(arylene ether sulfone)s are engineering thermoplastics that have been well-known since the p... more Poly(arylene ether sulfone)s are engineering thermoplastics that have been well-known since the pioneering studies of Johnson and Farnham et al. to have excellent mechanical and chemical properties. 16 They are used as films, coatings, membranes in ultrafiltration systems, ...

L'invention concerne une composition pour fil metallique contenant (A): de 0,1 a 20 % en poid... more L'invention concerne une composition pour fil metallique contenant (A): de 0,1 a 20 % en poids au moins d'un polyol a base de melamine obtensible par condensation de (A1) melamine, (A2) d'un aldehyde et (A3) d'un alcanolamine, (B): de 20 a 60 % en poids au moins d'une resine de polyester ou de polyesterimide, (C): de 20 a 90 % en poids d'un solvant ou d'un melange de solvants, (D): de 0 a 5 % en poids d'un catalyseur, ainsi que (E): de 0 a 1 % en poids d'un ou plusieurs additifs ou adjuvants, la somme des composants (A) a (E) donnant 100 % en poids.

Wire enamel composition comprising (A): 0.1 to 20 wt .-% of at least one available polyol melamin... more Wire enamel composition comprising (A): 0.1 to 20 wt .-% of at least one available polyol melamine-based by condensation of (A1) of melamine, (A2) an aldehyde and (A3) an alkanolamine, (B): 20 to 60 wt .-% of at least one polyester or polyesterimide resin, (C): 20 to 90 wt .-% of a solvent or solvent mixture, (D): 0 to 5 wt .-% of a catalyst, and (E): 0 to 1 wt .-% of one or more conventional additives and auxiliaries, wherein the sum of components (A) to (E) is 100 wt .-% is obtained.

Polymer, 2004

In continuation of our goal to determine the ability of CO 2 to plasticize acrylonitrile (AN) cop... more In continuation of our goal to determine the ability of CO 2 to plasticize acrylonitrile (AN) copolymers and facilitate melt processing at temperatures below the onset of thermal degradation, a systematic study has been performed to determine the influence of AN content on CO 2 absorption and subsequent viscosity reduction. Our previous report focused on the absorption of CO 2 in a relatively thermally stable 65 mol% AN copolymer. In this study, the ability for CO 2 to absorb in AN copolymers containing 85-98 mol% acrylonitrile was determined, and subsequent viscosity and equivalent processing temperature reductions were evaluated. Eighty five and 90 mol% acrylonitrile/methyl acrylate (AN/MA) copolymers were found to absorb up to 5.6 and 3.0 wt% CO 2 , corresponding to reductions of T g of 37 and 27 8C, and subsequent viscosity reductions of 61 and 56%, respectively. CO 2 absorption in these copolymers was found to occur immediately, in contrast to the time dependent absorption observed in the 65 mol% copolymer. An Arrhenius scaling analysis was used to determine the equivalent reductions in processing temperature resulting from the viscosity reductions, and reductions of up to 25 and 9 8C were observed for the 85 and 90 mol% AN copolymers. Based on the specific conditions used for absorption, no significant CO 2 uptake was observed for AN copolymers containing greater than 90 mol% acrylonitrile. Higher temperatures than those used here may be required to absorb CO 2 into AN copolymers containing greater than 90 mol% AN.

Journal of Applied Polymer Science, 2004

ABSTRACT In an effort to generate melt processable polyacrylonitrile (PAN) precursor fibers suita... more ABSTRACT In an effort to generate melt processable polyacrylonitrile (PAN) precursor fibers suitable for conversion to carbon fibers, an acrylonitrile/methyl acrylate (AN/MA) copolymer and two acrylonitrile/methyl acrylate/acryloyl benzophenone (AN/MA/ABP) terpolymers were synthesized at molar ratios of 85/15 and 85/14/1, respectively. The termonomer (ABP) was incorporated to accelerate crosslinking via UV irradiation, which serves to prevent relaxation of orientation and flow as the temperature of the fiber is raised during thermooxidative stabilization. Two molecular weights of the terpolymer and one molecular weight of the copolymer were studied to determine the effect of the termonomer, and the effect of molecular weight (MW), on the steady shear viscosity (η) and magnitude of the complex viscosity (η*). A higher rate of increase of η as a function of time was observed for the high MW terpolymer relative to that of the copolymer over the temperature range used. Using a temperature sweep and monitoring levels of η*, a minimum was observed at lower temperatures for both terpolymers. These results suggest that copolymerization with ABP significantly increased the thermally induced kinetics of crosslinking. Comparison of the η and η* data for the low and high MW terpolymers suggested that molecular weight also significantly reduced the melt stability (increased the kinetics of crosslinking). A chemorhelogical correlation was then used to quantify the effects of the termonomer and of molecular weight on the kinetics of crosslinking of the AN terpolymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2856–2865, 2004

Journal of Polymer Science Part A: Polymer Chemistry, 2004

Nonlinear monomer reactivity ratios for the homogeneous free-radical copolymerization of acryloni... more Nonlinear monomer reactivity ratios for the homogeneous free-radical copolymerization of acrylonitrile and methyl acrylate were determined from 1 H NMR and real-time Fourier transform infrared (FTIR) analyses. All 1 H NMR data were obtained on polymers isolated at low conversions (Ͻ10%), whereas the FTIR data were collected in situ. The copolymerizations were conducted in N,N-dimethylformamide at 62°C and were initiated with azobisisobutyronitrile. The real-time FTIR technique allowed for many data points to be collected for each feed composition, which enabled the calculation of copolymer compositions (dM 1 /dM 2) with better accuracy. Monomer reactivity ratios were estimated with the Mayo-Lewis method and then were refined via a nonlinear least-squares analysis first suggested by Mortimer and Tidwell. Thus, monomer reactivity ratios at the 95% confidence level were determined to be 1.29 Ϯ 0.2 and 0.96 Ϯ 0.2 for acrylonitrile and methyl acrylate, respectively, which were valid under the specific system conditions (i.e., solvent and temperature) studied. The results are useful for the development of acrylonitrile (Ͻ90%) and methyl acrylate, melt-processable copolymer fibers and films, including precursors for carbon fibers.

Macromolecular Materials and Engineering, 2008